For example, in regard to a printed wiring board for mounting electronic components, there has been a demand for speeding up and density increase in the mounting of materials for forming electroconductive wiring, along with the requests for size reduction, thickness reduction, and weight reduction of electronic equipment and an enhancement of productivity.
In this regard, attempts have been made to form silver wiring at lower temperatures using an ink having nano-sized fine silver particles dispersed therein, for example, by an inkjet printing technology.
In this case, printing a desired circuit shape using an ink containing fine silver particles, and binding the fine silver particles in the coating film by sintering to obtain a thin film may be considered; however, in view of the heat resistance of substrates, there is a demand for a fine silver particle-containing ink that can be sintered at a temperature close to 100° C. Furthermore, since silver wiring is used, lower volume resistance is demanded, and in order to do so, it is demanded that the surface be as smooth as possible.
For example, Patent Document 1 suggests an ultrafine metal particle dispersion liquid in which fluidity is maintained even at a high concentration, and ultrafine metal particles can be flocculated and concentrated, and a method for production thereof.
This is an ultrafine metal particle dispersion liquid in which ultrafine metal particles having a particle size of 100 nm or less are dispersed, using one or more of an alkylamine, a carboxylic acid amide, and an aminocarboxylic acid as dispersants.
However, this Patent Document 1 has no disclosure on the sintering temperature, and when the inventors of the present invention conducted an experiment, it was found that a sintering temperature far higher than 100° C. was needed.
Furthermore, Patent Document 2 discloses a method for producing an ultrafine silver particle colloid by mixing a silver salt, a reducing agent that does not exhibit a reducing ability in an organic solvent, and an alkylamine in an organic solvent.
It is said that this ultrafine silver particle colloid has an average particle size of 1 to 20 nm and is monodisperse, the particles are polygonal and have a uniform shape, and the colloid is suitable as a material for a low temperature sinterable saline paste or the like. However, there is no disclosure on a specific sintering temperature, and according to an experiment of the inventors of the present invention, the sintering temperature was definitely far higher than 100° C. as expected.
Furthermore, there is no disclosure on the surface roughness of the sintered bodies of Patent Documents 1 and 2, and it has been confirmed that both have matte surfaces, and the volume resistance of the sintered bodies are more than 30 μΩ·cm at a film thickness of about 500 nm in terms of weight.